(a) Field of the Invention
This invention relates to the treatment of aqueous cellulose pulp in the pulp and paper industry; more especially the invention is concerned with a method and apparatus for detecting gas parameters in such a treatment.
(b) Description of the Prior Art
The treatment of cellulose pulp in the manufacture of paper includes several stages; the later stages include chemical bleaching operations which typically employ chlorine-based chemicals, for example, chlorine dioxide and sodium hypochlorite. Such bleaching operations can be carried out under conditions in which very little of the lignin still remaining in the pulp fibres after earlier delignification stages is removed, as well as under conditions in which the delignification is substantially completed.
Consumption of chlorine-based chemicals in the bleaching of pulp is considerable and costly, additionally it produces chloro-organic compounds as side products which represent a disposal problem. Many of the chloro-organic compounds are of complex structure, not readily broken down and are potentially hazardous or in any event raise concerns as to their long term effect on the environment.
In order to reduce the consumption of chlorine-based chemicals in the bleaching operation, oxygen is used in oxygen delignification and oxygen extraction stages in the treatment of pulp, which stages precede the bleaching operation; in both the oxygen delignification and extraction stages delignification of the pulp fibres is achieved.
The oxygen delignification and oxygen extraction processes both involve dispersion of oxygen in the aqueous cellulosic pulp under pressure. The dispersed oxygen is absorbed and reacts as the pulp flows upwardly through a vertical reactor or retention tube. In the case of medium consistency pulp, which contains 8-12%, by weight, of cellulose solids, the dispersing of the oxygen in the pulp is achieved, for example, by means of a medium consistency mixer or a gas diffuser having a high velocity of pulp passing across it.